Presensitized printing plate and method for preparing same



United ees Patent -2,946,683 I PRESENSITIZEDPRINTINGPLAT ANDMETHOD FOR PREPARING SAME Ibei-t 'aMellan, Bayside, :and Robert Gumbinner, --Tarrytown, N.Y., assignors to Polychrorne Corporation, Yonkers, N .Y., acorporation-of N eW-York N Drawing. Filed Dec. 29, 1958, Ser. N05783I55 17 Claims. (Gl. 96--75) This invention relates to a new and imprdvediplanographic printing plate and a novel method of makmg such ai-plate. I

The art of .p'lanographic rprinting depends upon the imrniscibility of grease and water and upon the preferentialiretention of a greasy im'age forming substance by theiimage areas, and a similar retention-bf an aqueous dampening fluid by the non-image areas. When angreasy image is imprinted on a suitable surface, and the entire .surfaceiis then moistened with an-aqueous solution, the image areas "will repel the Water, and :thenon-image areas will retain the water. Upon "subsequent-application of :greasy ink, the imagefportions retainthe ink,whereas the moist, non-image areas repe'l it. T-lreimage is'then transferred "to -:paper or cloth, via an intermediary, so .called off-set cylinder, which is necessary to prevent mirror :image zprinting.

1n thecase of'presensitizedplates, aiplate with alight sensitive coating is "exposed tolight through anegative, and the' image portion-ofuthe plate becomeshardened and madeinsoluble in waterbythe action ofthe light. The unexposed light-sensitive coating :is "then removed by a desensitizing solution leaving awater-receptive or hydro- :philic underc'oating as thenon image area.

It 'has been known to use, as the base material in a .presensitizedplate, either awaterproofed paper .or a fi'exible sheet of metal. Typical metals which'iriaybe used are aluminum, steel, zinc, magnesium, chromium and copper.

Because paper is relatively coarse :lgrained and base. tendency to stretch, a plate having a metallic 'base'will give finer reproduction and longer service than will a paper-base plate. In "coating =a metallic plate with a light-sensitive material, however, it is necessary to. provide the metal with a hydrophilic surface to'which the light-sensitive material will adhere, it will not adhere to the bare metal. In the prior "art this has been accomplished by various methods including coating the-metal with a hard siliceous layer appliedby treatment with an alkali silicate.

Such -a siliceous hydrophilic underc'oating, however, raises certain problems which have'beenovercome by the present invention. For example, a silicated plate often has limited shelf life and limited water-receptivity. It may also tend to absorb moisture giving it a lack of stability in moist, warm atmospheres, thereby creating packaging and storing problems under these conditions. Moreover, a silicate coating can often result in a-plate in which the number of true-copies which-can bemade are limited.

In accordance with the present invention, it has been found that a presensitized metal baseplanographic printingqplate may be made which does notinvolve the problems arising from the use of a silicate undercoating. This is accomplished by treating the metallic surface with-an aqueous solution of a zirconium hexahalide, preferably potassium zirconium fluoride.

The novel 'hydrophi-lic surface formed by this treatment 2,946,683 Pal-tented July 26, 1960 tion with the albumen, ammonium bichromate or 'other coatings which are used ininstances-where the zprinter or l-ithographer applies his own light=sensitive material.

-Accordingly,- it -is -an-obj cot of thisginvention to provide a novel -hydrophilic coating -;for a light sensitiverplate of the type comprising a metallic base and a light sensit'ive material. I I

Another-object of this :invention isto provide -a-:presensitized aluminum plate havinganovel'hydrophilic coating which readily adheres to thealuminum, tenaciously holds an overlying light-sensitive material and is highly water receptive. I 7 V Another object of-tlais invention is'to provide -a presensitizedplate which, by virtue of-its novel-hydrophilic coating has long shelf life and provides" long runs of clear, detailed images.

Still another object of this invention is to? provide a noveland economical methodforpreparinga plate having such characteristics. I M r These and other objectsofthe-present =invention will be more clearly understood frorn'the description which follows: 7

Essentially, the present' invention involves a planegraphic. printing :plate con'iprising a -metallic base, -'a "hydrophilic coating thereonp'rovidedby treatment with an aqueous-solution of a zirconium hexahalide and a lightsensitive surface coating. 7 V

In -a more specific and preferred embodiment, this invention involves the preparation of an aluminum base plate: by treatmentwith an aqueous solutionof potassium zirconium fluoride .(K ZrE which reacts with-the surface ofthe-aluminum to .give a highly "desirable and permanently 'hydrophilic; coating to which -a light-sensitive material, such as a diazo resin, will tenaeiously adhere.

In accordance with the .present invention, it has *be'en found --th-at when one -or both surfaces of -a sheet of aluminum, after being degreased and,.preferably acidetched and cleaned, is imrnersedinto an aqueous solution of. potassium zirconium fluoride, the sur ace becomes hydrophilic and receptive to a light-sensitivadyeor resin, and that an image may .be providedon'thesurfaceby exposure ofselectedportions thereof to 'light. As in 'the case of other presens'itized plates, "the light-altered dye. preferably a diazo resin, forms 'a'per-man'ent image. The unconverted light-sensitive material is removed by a .desensitizer, and the almost invisible image 'is then developed by means of a suitable lacquer. Fhe resulting image is strong and holds tightly-to the:plalte. The'plate can then be placed on -a pressand a large number of copies made.

The treatment with potassium zirconium fluoride is preferably followed by -a hot 'watertreatment which' appears to complete the chemical reaction between the K ZIF and the surface of the aluminum. While th'is treatment can take place within various limits 'kif' t-iine, temperature and concentration, the concentration of K Zr-F should generally "be between 'ilil iperc'ent, by weight, and a saturated solution (about 8:7 viper'cnt at 60 C.). It is particularly preferred that -theconcentration be between about-0.3 to 1.0 percent.

The time of immersion may vary from-as little asrt'wo secondsto as much as ten minutes. Generally, a one to three minute interval is preferred for optimum'-1:fro essing economies. The 'temerature may vary between limits of about from 90 F. and 160 F. with favorable results being obtained at a temperature of 150 F. Naturally, temperature, time and concentration are interrelated and various combinations within theranges her in set forth can be effectively utilized.

The hot water treatment which follows the immersion of the aluminum K ZrF involves the use of water at elevated temperatures between about 100 and 190 F. The temperature varies with the time of immersion which may be between about one and five minutes. It has been found that good results are obtained with a water temperature of about 150 F. and an immersion time of about between one and three minutes.

The resulting coating or layer is in the form of a continuous film, as distinguished from crypto-crystalline zirconia particles which have been formed on plates of the prior art.

Without being bound by any particular theory, it is presumed that the clean aluminum surface which is exposed to the K ZrF forms a reaction product of K A1F and K ZrF It is preferred that prior to this treatment, the surface of the aluminum be activated by chemical etching with various acids so that a more strongly adhering image can be obtained. Consequently, the pretreatment of the aluminum will preferably involve not only an alkali degreasing agent, an acid etch, and a desmutting operation, but also a pre-treatment with an acid such as phosphoric acid, chromic acid, nitric acid, sulphuric acid or oxalic acid which activates the aluminum surface, and makes it more receptive to the subsequent treatment with aqueous K ZrF In this connection, it is preferred to use either phosphoric acid or oxalic acid of a concentration in the range from about .01 percent to about 5 percent, by weight, although the narrower range of 0.2 to 1 percent is generally most desirable. The time of immersion may also vary between about one second and three minutes with five to ten seconds giving good results, depending on the concentration and time. The temperature can also vary between about 50 F. and 100 F. with 65 F. providing a suitable treatment. It should be noted that, here also time, temperature and concentration are all inter-related and various combinations within the limits stated can be used. There is some danger in having the concentration of the acid too high because, under these conditions, a pitting of the plate may take place. Some acids, such as sulphuric acid, which tend to attack aluminum faster, would be utilized at lower temperatures and for shorter contact times in obtaining optimum results.

Among the water-soluble zirconium hexahalide compounds with which the metal base is treated, it has been found that the hexafluorides are the most readily available and that K ZrF has produced particularly desirable results. Also suitable are CaZrF and (NH ZrF although treatment with these compounds tend to produce plates of more limited shelf life.

After the surface coating resulting from the aqueous zirconium hexahalide treatment is formed, the hydrophilic surface may then be hardened in a bath of a watersoluble organic acid,- such as citric or tartaric acid and preferably citric acid. This is similar to the hardening treatment set forth in U.S. Patent No. 2,922,715, which is owned by applicants assignee. In hardening the hydrophillic layer, the plate may be clipped in a dilute solution of citric acid of preferably between about 0.1 percent to 5 percent, by weight, and the temperature between about 50 F. and 100 F., the time of immersion varying between about one second and five minutes.

The metallic base which is preferably aluminum is prepared for the silicate treatment either by etching the same with acid and alkali or by graining. Typical acid-etching treatments are known to the prior art and, for example, described in detail in U.S. Patent No. 2,882,153.

If instead of the above, a grained plate is desired, the graining may be performed by any of the mechanical means well known in the art, e.g. by rubbing with an abrasive, sandblasting or brushing with a wire, nylon, or hair brush. Details of mechanical graining methods are found in the prior art, e.g. see U.S. Patent No. 2,882,154.

After the hydrophilic coating is on the plate, there may be applied thereto various light-sensitive compounds. If the plate is to be of the type in which the lithographer applies the light-sensitive material, such material would be, for example, albumen bichromate. In making a presensitized plate, the light-sensitive material typically would be one of the well known diazo resins which have been found, upon exposure to ultra-violet light, to be sufficiently light-hardenable to be useful in planographic printing processes.

A typical compound as previously mentioned is the condensation product of paraformaldehyde and paradiazodiphenylamine. The sensitizer may comprise one percent diazo and 0.1 percent of a 10 percent solution of saponin. In using the light-sensitive diazo resins, it is also possible to provide an anti-oxidant in the form of hydroquinone which would be added to the hardened silicate layer prior to diazo treatment. The hydroquinone may be applied as a .01 to 0.1 percent aqueous solution.

The following is a specific example of the method for preparing an improved aluminum presentized plate in accordance with the present invention:

A sheet of 38 aluminum (99 percent purity) is degreased, etched, and rinsed with water in accordance with well known techniques. It is then dipped in 0.2 percent phosphoric acid, by weight, for five to ten seconds at a temperature of 65 F. The plate is then removed from the bath, permitted to drain for a minute and then immersed in a solution of 1 percent potassium zirconium fluoride at about 150 F. for a period of three minutes. The above procedure may also be performed using 0.5 percent oxalic acid, instead of the phosphoric acid.

The aluminum sheet is then removed from this bath and permitted to drain for one minute. It is then immersed in hot water at about 150 F. for three minutes.

. formed on the surface of the plate.

The plate is then removed from the hot water and permitted to drain for one minute, and then immersed in a one percent solution of a citric acid at 65 F. forthree minutes. The plate is then removed from the citric acid solution, rinsed with water, dried, and a solution of a light-sensitive dye is applied to both sides of the aluminum sheet. The light-sensitive material is the condensation product of paraformaldehyde and paradiazodiphenylamine (four parts of formaldehyde to thirty parts of paradiazodiphenylamine, by weight). The plate is coated on both sides, retaining about 0.25 cc. of diazo solution per side. After drying the plate is ready for use.

Upon exposure to a source of ultra-violet light through a negative, a strong water insoluble tenacious image is The plate may be subjected to vigorous testing, and upon removal and redeveloping of the image five times, the plate is put on the printing press and 2,500 sharp and clear copies are run.

In the foregoing, the present invention has been described only in connection with preferred embodiments thereof. Many variations and modifications of the principles of the invention within the scope of the description herein are obvious. Accordingly, it is preferred to be bound not by the specific disclosure herein, but only by the appending claims.

We claim:

1. A presensitized planographic printing plate comprising a metallic base and a hydrophilic coating thereon in the form of a continuous film, said coating being provided by treatment of the metal base with an aqueous solution of a zirconium hexahalide, and a light sensitive diazo coating overlying said hydrophilic coating.

2. A presensitized planographic printing plate comprising an aluminum base, a hydrophilic coating thereon in the form of a continuous film, said coating being provided by treatment of the aluminum base with an aqueous solution of K ZrF and a light-sensitive diazo coating, overlying said hydrophilic coating.

3. A presensitized planographic printing plate comprising an acid treated aluminum base and a hydrophilic coating thereon in the form of a continuous film, said coating being provided by treatment of the aluminum base with an aqueous solution of a zirconium hexahalide and a light sensitive diazo coating overlying said hydrophilic coating. 1

4. A presensitized planographic printing plate comprising an aluminum base, a hydrophilic coating thereon in the form of a continuous film, said coating being provided by treatment of the aluminum base with an aqueous solution of a zirconium hexahalide and a light-sensitive diazo surface coating overlying said hydrophilic coating.

5. The method of preparing a presensitized metallic base planographic printing plate comprising treating the metallic surface with an aqueous solution of a zirconium hexahalide so as to form a hydrophilic surface thereon and then coating said hydrophilic surface with a lightsensitive diazo compound.

6. The method of claim 5 in which the metallic surface is treated with a zirconium hexafluoride.

7. The method of preparing a presensitized aluminum base planographic printing plate comprising treating the aluminum surface with an aqueous solution of K ZrF at elevated temperatures so as to form thereon a hydrophilic surface and then coating said hydrophilic surface with a light-sensitive diazo compound. 7

8. The method of claim 7 in which the treatment with K ZrF is performed at a temperature between about 90 F. and 160 F. and the solution has a concentration of at least 0.1 percent K ZrF by weight.

9. The method of claim 8 in which the treatment with K Z1'F is followed by a treatment with hot water between 100 F. and 190 F. for between about one and five minutes.

10. The methodof claim 9 in which the surface of the aluminum is acid etched by pre-treatrnent with phosphoric acid prior to the treatment with K ZrF 11. The method of preparing a presensitized aluminum base planographic printing plate comprising treating the aluminum surface with an aqueous solution of K ZrF at elevated temperatures so as to form thereon a hydrophilic 13. The method of preparing an aluminum base plane graphic printing plate comprising treating at least one surface of a sheet of degreased aluminum with an aqueous solution of an acid from the group consisting. of phosphoric acid and oxalic acids and then rendering said acid-treated surface hydrophilic by a subsequent treatment with an aqueous solution of K ZIF at elevated temperatures, hardening the surface coating produced by said K ZrF treatment by the application of a citric acid solution thereto, and then applying to said plate an aqueous solution of a light-sensitive diazo compound.

14. The method of preparing an aluminum base planegraphic printing plate comprising treating at least one surface of a sheet of degreased aluminum with an aquesurface, hardening said surface with a citric acid treatment, and then coating said hydrophilic surface with a light-sensitive diazo compound.

12. The method of preparing an aluminum base pianographic printing plate comprising treating at least one surface of a sheet of degreased aluminum with an aqueous solution of an acid from the group consisting of phosphoric and oxalic acids and then rendering said acidtreated surface hydrophilic by a subsequent treatment withan aqueous solution of K ZrF at elevated temperatures and then applying to said plate an aqueous solution of a light-sensitive diazo compound.

ous solution of phosphoric acid of a concentration in the range of .01 percent to 5 percent for between about one second and three minutes at a temperature between 50 F. and 100 F., and then rendering said acid-treated surface hydrophilic by a subsequent treatment with an aqueous solution of K ZrF of a concentration between'.01 percent to saturated, at a temperature between F. to 160 F. for one to three minutes and then applying to said plate an aqueous solution of a light-sensitive diazo compound.

15. The method of preparing a presensitized aluminum base planographic printingiplate comprising treating at least one surface of a sheet of degreased. aluminum with an aqueous solution of phosphon'eacidof a concentration in the range of .01 percent to 5 percent for between one second and three minutes at a temperature between 50 F. and F., and then rendering said acid-treated surface hydrophilic by a subsequent treatment with an aqueous solution of K ZrF of a concentration between .01 percent to saturated, ,at a temperature between 90 F. to F. for one to three minutes, soaking said sheet in hot water of a temperature between 100 F. and F. for one to five minutes, and hardening the surface coating thereon by treatment with an aqueous solution of citric acid and then applying to said plate an aqueous solution of a light-sensitive diazo compound, 7

16. The method of claim 15 in which the K ZrF treatment is performed with the concentration of phosphoric acid being between about 0.2 percent and 1 percent and the concentration of citric acid being between about 0.1 percent to 2.4 percent.

17. The method of claim 15 in which the aluminum sheet is treated with a 0.2 to 1. percent solution of oxalic acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,814,988 Bradstreet et al. Dec. 3, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,946,683 July 26, 1960 Ibert Mellan et. a1.

It is herebjr certified that error appears in the-printed specification of the above "numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Coiumn 3., line 70, for "silicate" read aqueous zirconium liexahallde column 4, line 22, for "silicate" read hydrophi- Signed and sealed this 31st day of January 1961.

( SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner of Patents 

1. A PRESENSITIZED PLANOGRAPHIC PRINTING PLATE COMPRISING A METALLIC BASE AND A HYDROPHILIC COATING THEREON IN THE FORM OF A CONTINUOUS FILM, SAID COATING BEING PROVIDED BY TREATMENT OF THE METAL BASE WITH AN AQUEOUS SOLUTION OF A ZIRCONIUM HEXAHALIDE, AND A LIGHT SENSITIVE DIAZO COATING OVERLYING SAID HYDROPHILIC COATING. 